The position recognizing method for detecting the position of an object from a contrast image imaged by an image pickup device is widely used in visual recognition device of robots in various production facilities.
Of the position recognizing method used in such facilities one example of, a prior art device for recognizing the position of a screw hole is described below.
FIG. 5 is a block diagram showing a construction of a position recognizing apparatus utilizing a conventional position recognizing method, in which the central position of a circular object, being a screw hole, is detected. In FIG. 5, reference numeral 20 is image pickup means for picking up an object (not shown) and issuing a video signal, 21 is contrast image memory means for storing the video signal obtained from imaging with the image pickup means 20 as contrast image data, 22 is contrast image scanning means for scanning the contrast image data by a contour scanning window A described later, thereby obtaining scanning data. Reference numeral 23 is position calculating means for calculating the position of the object by using the scanning data.
FIG. 6 shows a construction of the contour scanning window A used in FIG. 5, and in FIG. 6 reference numeral 24 is a contour scanning circle having a diameter equal to the contour of the circular hole in the object, and 25 is a concentration correlation line for measuring the image concentration inside and outside of the contour scanning circle 24, orthogonal to the contour scanning circle 24, and the contour scanning window A is a window comprising a plurality of concentration correlation lines 25.
The position recognizing operation in the position recognizing apparatus in FIG. 5 is explained below as an application in the contour scanning window A in FIG. 6.
The video signal (image data) issued from the image pickup means 20 is stored in the contrast image memory means 21. This is the image data of the circular object, and it is scanned by the contrast image scanning means 22 in the contour scanning window A shown in FIG. 6, and position is calculated by the position calculating means 23 in every concentration correlation line 25, and the position of the contour scanning window A where the number of concentration correlation lines 25 of which value is greater than the threshold is maximum is detected as the position of the circular object.
In this case, the position calculating means 23 calculates the absolute value of the difference between the measured concentration value of a point inside the contour of the object on the concentration correlation line 25, and the measured concentration value of a point outside the contour of the object.
In the conventional method of recognizing the position, however, there are problems. When tightening plural screws from the contrast image data imaged from the top of the workpiece shown in FIG. 2, if the deviation between upper and lower holes was large, then the screw tightening operation was stopped. Each screw hole would then need to be evaluated so that the screws could be tightened. Hence, much processing time was spent performing position recognition.
The invention is intended to solve the problems of the prior art, and it is hence an object thereof to present a method of recognizing a screw hole and screwing method based on the recognition for detecting the deviation of an upper hole in an object and a lower hole in an object of pairs of holes, tightening the screws sequentially from the one of smaller deviation, and tightening all screws. Or detecting the deviation angle of the object to be tightened after detecting positions of two points, calculating the deviation of other holes, and tightening at high speed.